Polyvinyl chloride (PVC) is a thermoplastic polymer that is widely used in the manufacture of a variety of commercial products, including building materials, plumbing pipe, clothing, upholstery, flooring and vinyl records, to name just a few examples. PVC is synthesized by free radical polymerization of vinyl chloride monomer using a monomer-soluble initiator or catalyst. Some of the known initiators are azobisisobutyronitrile, tertiary butyl hydroperoxide, lauroyl peroxide, benzoyl peroxide and isopropylperoxy dicarbonate. A batch suspension preparation generally contains about 0.01 to 1.0 wt % vinyl chloride monomer at a pH of about 7-9. Polymerization is commenced by dissolving the initiator in the monomer solution and heating at a temperature in the range of about 35° to 75° C. for about 2 to 12 hours, with constant agitation of the reactants. The process is completed when one of the detached hydrogen atoms attaches to the unpaired electron at the end of the PVC chain, or when the carbon atoms form a double bond through a process called disproportionation, which results in the free hydrogen atom.
The free radical polymerization of vinyl chloride monomer is generally considered to be the easiest and most economical method today of synthesizing PVC, despite the fact that the polymerization process can also cause impurities and defects in the polymer. Due to the unpredictable nature of free radical polymerization carbon-hydrogen bonds are sometimes broken instead of only the carbon-carbon bonds of the monomers, leading to the occurrence of branching at sites on the growing polymer strand where the carbon-hydrogen bond was broken. Another challenge associated with some PVC synthesis reactions is the amount of unpolymerized monomer that sometimes remains after the polymerization reaction ceases. Many existing processes and production facilities for producing polyvinyl chloride are also subject to various constraints such as mass flow limitations, product yield, plant size and energy consumption. Accordingly, there is continuing interest in developing ways to improve the selectivity and yield of polyvinyl chloride from free radical polymerization of vinyl chloride monomer.